10
Solvent/Oil-based Inks
Solvent-based inks are commonly used in industrial
marking or coating applications where the printing is
done on a nonporous substrate such as plastic, metal,
or glass. Because no absorption or penetration
occurs, the printed image relies on quick evaporation
of the ink solvent to be fixed onto the substrate.
However, there are several disadvantages to these
types of inks, solvent inks tend to emit a strong smell
and over time the printed area can smudge. These
inks also have environmental and health and safety
issues, for example, inks that contain petroleum
solvents emit volatile organic compounds (VOCs) into
the air. VOCs can be an irritant for printshop workers
when present in the form of vapours, and also
contribute to the formation of smog. Inhalation of the
solvent can cause drowsiness and hallucinations and,
amongst other things, can be carcinogenic. Of course,
these solvent vapours cause environmental problems
when released in to the atmosphere and can be
flammable and there is substantial pressure on ink
manufacturers to develop solvent recovery and
incineration systems but the development of solvent
free inks remains the popular option.
Another more recent, non-aqueous ink option is oil-
based ink. More often found in large-format inkjet
printers (several of which utilize Nu-Kote piezo shear-
mode print heads) the use of non-polar oil-based ink
minimizes the effect of electrical fields on the ink and
print head materials. There are also legitimate claims
that with some coated media, oil-based inks enjoy
faster drying time and the absence of cockle on paper
substrates, when compared with water-based inks.
Wax/Polymer-based Inks
Solid (hot-melt) ink, as referred to in the Inkjet
Technology Overview, is usually solvent-based and is
effectively solid at room temperature. This ink is jetted
out from the print head as a molten liquid and, upon
hitting a recording surface, the molten ink drop solidifies
immediately, thus preventing the ink from spreading or
penetrating the printed media. The quick solidification
feature ensures that image quality is good on a wide
variety of recording media.
Inkjet image quality and durability for water-based,
solvent and oil-based inks are generally acceptable
when they are printed on inkjet papers or coated
substrates. But when printing on non-absorbent
substrates such as metal, glass and plastic, these types
of inks are generally unable to produce durable and
sharp images. To solve this, the idea of using UV-
curable, wax or polymer-based inks was discussed for a
long time. But factors relating to inkjet print head
capability, photo-initiator and low-toxicity monomer
availability, hindered the progress of UV-curable inkjet
ink development. Today, with recognised increases both
in the capability of and availability of inkjet print heads,
and with UV photoinitiators, monomers and even
oligomers readily available at economic scale, successful
development of UV-curable inkjet inks is on the horizon.
